This invention relates to a method of enhancing the activity of high silica containing crystalline materials by a process which involves hydrothermal contact with solutions containing metallate anions at a pH of at least 7 so as to cause the metal in the solution to become associated with the high silica containing crystalline material and to enhance its activity.
High silica containing zeolites are well known in the art and it is generally accepted that the ion exchange capacity of a crystalline aluminosilicate is directly dependent upon its aluminum content. Thus, for example, the more aluminum there is in a crystalline structure, the more cations are required to balance the electronegativity thereof, and when such cations are of the acidic type such as hydrogen, they impart catalytic cracking activity to the crystalline material. On the other hand, high silica containing zeolites having little or substantially no aluminum have many important properties and characteristics and a high degree of structural stability such that they have become candidates for use in various processes including catalytic processes. Materials of this type are known in the art and include high silica containing aluminosilicates, such as ZSM-5 (U.S. Pat. No. 3,702,886), ZSM-11 (U.S. Pat. No. 3,709,979), and ZSM-12 (U.S. Pat. No. 3,832,449) to mention a few.
The silica-to-alumina mole ratio of a given zeolite is often variable; for example, zeolite X can be synthesized with a silica-to-alumina ratio of from 2 to 3; zeolite Y from 3 to about 6. In some zeolites, the upper limit of silica-to-alumina ratio is unbounded. ZSM-5 is one such example wherein the silica-to-alumina mole ratio is at least 12. U.S. Pat. No. 3,941,871 discloses a crystalline metal organo silicate essentially free of aluminum and exhibiting an X-ray of diffraction pattern characteristic of ZSM-5 type aluminosilicates. U.S. Pat. Nos. 4,061,724, 4,073,865, and 4,104,294 describe microporous crystalline silicas or organo silicates wherein the aluminum content present is at impurity levels.
Because of the extremely low aluminum content of certain silica containing zeolites, their ion exchange capacity is not as great as materials with a higher aluminum content. Therefore, when these materials are contacted with an acidic solution and thereafter are processed in a conventional manner, they are not as catalytically active as their higher aluminum containing counterparts.
There are many patents and technical articles relating to contacting crystalline aluminosilicate zeolites as well as high silica containing materials having substantially no aluminum with solutions of aluminum ions in order to base exchange the aluminum for the cations originally associated with the crystalline materials. Additionally, it is known to incorporate a high silica zeolite into a matrix or binder wherein such processing also involves contacting said crystalline material with aluminum ions. Typical patents concerned with the above techniques would include some of the patents already mentioned, i.e., ZSM-5, ZSM-11, ZSM-12, as well as U.S. Pat. Nos. 3,140,329, 3,629,152, 3,429,830, 3,562,148, 3,582,497, 3,410,808, 3,403,110, merely to mention a few. The novel process of this invention is not concerned merely with a process for incorporating a crystalline zeolite in a binder matrix nor is it concerned with a simple ion exchange process. Rather, it is concerned with a novel process for enhancing the acid activity of a crystalline material. In the prior art previously referred to, there is no teaching of treatment of a ZSM-5 type crystalline material with a solution containing aluminate ions in order to enhance the activity of a crystalline material.